Our view of phytoplankton has historically revolved around their inability to
control their location in space. The term phytoplankton itself underscores this
particular difference between phytoplankton and their sessile terrestrial counterparts.
Yet there are other differences between land plants and the phytoplankton that are
perhaps equally important, beyond this sessile-planktonic dichotomy, to their growth, survival, and productivity. For example, phytoplankton are microbes and thus are short-lived, with generational scales on the order of days or less. An intriguing
question to ask is how today’s pelagic ecology would differ, had this temporal
difference between plants and phytoplankton been initially emphasized, perhaps by
naming these microbes phytoephemera instead? This dissertation addresses certain
aspects of the ecology of phytoplankton that result from their having short generational scales. Because they are so short lived, phytoplankton need to adjust their photosynthetic physiology to cope with more rapid changes in irradiance than may
matter to longer-lived plants. Photoacclimation on the hours-plus time scales has been studied extensively in the phytoplankton, because its temporal scales match those of vertical mixing processes in the ocean. Yet most phytoplankton exhibit faster photosynthetic responses as well, down to the time scales of seconds. These
photosynthetic responses have received considerably less attention in phytoplankton
ecology. This dissertation specifically examines these rapid, seconds-to-hour scale
photosynthetic responses in phytoplankton. First, the physiological bases of rapid
photosynthetic regulation were examined using a numerical model that shows how
specific physiological changes in phytoplankton photosystems either constrain or enhance light harvesting. This model is stochastic, and thus replicates certain
nonlinear aspects of light harvesting better than equation-based analytical models.
Also in this dissertation, a laboratory study is described that examined rapid
photosynthetic regulation in three model phytoplankton. Results suggest that rapid
photosynthetic regulation is not only constrained to higher eukaryotic phytoplankton, but also occurs in the two dominant marine photosynthetic prokaryotes,
Synechococcus and Prochlorococcus. Finally, rapid photosynthetic responses were
examined in field assemblages at Station ALOHA in the North Pacific. This ocean
region experiences considerable cloud cover, which may result in a strong degree of
rapid photosynthetic responses, even in near-surface assemblages.

Genre

Thesis

Topic

phytoplankton

Identifier

http://hdl.handle.net/1957/3052

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